The floor of the New York Stock Exchange was transformed last night by the unlikeliest of sponsors, a 19-year-old French prodigy known to most as the launchpad-wielding Madeon. For just over an hour, the heart of the world economy pulsed, not with stock tickers and screaming traders, but with a barrage of pad-triggered clips, arranged to create a symphony of electro-pop that shook the foundation of Wall Street’s trading floor.